Method of making laminated products



Pasta Au .8, 1937 UNITED STATES PATENT OFFICE 1,089,034 n v l Ms'rnon OF MAKING LAMINATED" PRODUCTS i James V; Nevin, Aberdeen, I v No Drawing. App ication August 12, 193

Serial No. 35,885

3 Claims. (Cl. 144-309) This invention relates to a method of making laminated products, and more particularly to a method of making plywood using a fibrous web impregnated with an aqueous resin-forming binding agent to effect a bond between the constituent laminations of the plywood.

It has heretofore been proposed to impregnate fabrics and the like with solutions of; a

synthetic resin of the phenol-aldehyde type in an I have new found that if the resin forming:

binding agent is made up into an aqueous solution and the fibrous web impregnated therewith, the cost of manufacture is greatly reduced and the difllculties due to the formation of vapor pressure pockets is largely eliminated. I have also found that a firmer and more satisfactory bond is obtained if the impregnated web is humidified to a substantial moisture content before being interposed between the other laminations and inserted in the hot presses. The layer or film carrying the binding agent may also be used as a surface coating for the faces of either plywood or fiber board panels when a smooth surface is desired.

' It is therefore an important object of this invention to provide a method for making laminated products wherein a carrier film or web impregnated, with an aqueous solution of a binding agent is employed as the bonding medium for wood veneers or wood fiber board, or as a surface layer therefor.

It is also an important object of this invention to provide a method for the manufacture of plywood and the like which includes the use of a carrier film or web impregnated with an aqueous solution of a resin-forming binding agent and wherein the impregnated carrier film is humidiiled prior to the hot pressing operation and the product coming from the hot presses is again come apparent from the following description and appended claims.

The carrier film or web that I impregnate with an aqueous solution of a resin-forming binding agent may be'any suitable porous, flexible,fibrous 5 sheet material, such asa fabric or an unsized paper. Unsized kraft paper or toweling has been found to be particularly suitable, since it has sufficient wet strength to withstand the slight tension to which it is subjected after it hasbeen, 10 saturated with the aqueous binder solution. The paper may be either bleached or unbleached.

In order to impregnate the carrier film or web, it is conducted through a set of pressure rolls, one

' or both of which are immersed in a very viscous 15 aqueous solution of the resin-forming binding agent. As the carrier film; passes between the pressure .rolls, the aqueous solution of the, binding agent is forced directly into the absorbent film. The viscosity of the aqueous solution of the 20 binding agent can be. adjusted so as to give either a light or heavy coating or impregnation, as desired. v

After impregnation of the carrier fllm .or web with the aqueous solution of the binding agent,

the impregnated carrier film is dried, preferably at a temperature of from 120 to 215 F. and stored until ready for use. Prior to using the carrier film; it is passed through a humidifying apparatus at a temperature of about 100 F. in an atmosphere of about to relative-humidity for such time as is required to impart to the impregnated carrier film a moisture content of from 20 to 40%. g

The film is then in a limp condition and should 35 be laid between the sheets to be laminated and subjected to the hot pressing operation as soon as possible thereafter. Either wood veneer or wood fiber board may be used as the constituent lamination in the manufacture of plywood or 0 other laminated product. I 1

Upon the application of heat and pressure in the hot press, the resinous material with which the carrier film is impregnated fuses and is converted into ahard, infusible resin. Due to the 45 fact that the resinous material of the carrier film contains the proper amount of moisture, a certain amount of steam will be formed under the, influence of heat and serve as a carrier for the fused resin. As ,theprocess takes place under 50 constant pressure, the resin binder is forced into the constituent laminations in a fused state in both directions. Upon the continued application of heat, the fused resin sets into a hard infusible and insoluble compound. If the film does not contain suillcient moisture, the penetration of the binder into the wood is limited, owing to its dry state, and the resulting bond will be inferior.

In the hot pressing operation best results are ii obtained by the use of temperatures between 315' and'335 l"., and pressures ranging between 100 lbs. and 250 lbs. per sq. in. The time required will, of course, depend upon the temperature and the thickness of the plywood panel being made.

but in general will vary between 2% and 80 min utes.

The hot panels coming from the hydraulic press are immediately taken to humidifying apparatus, where they are piled between racks and 16 weighted to keep them flat. The humidifying apparatus is then operated at a temperature of about 190 1'. and at a relative humidity of 80 to 90%, the length of time in the humidifying equipment depending upon the thickness of the ply- 20 wood panels and themolsture content desired in the panels. In general, it is dais-able to impart to the panels a moisture content of between 8 and 12%. With this moisture content the plywood panels will not be subject to much change when exposed to the relative humidities occurring in most localities in which plywood panels are used.

The aqueous dispersion oi the binding material may be prepared from various ingredients capable of forming synthetio resins of a hard, infusible character. Examples of suitable synthetic resins are those of the phenolic-aldehyde and urea? aldehyde type, or mixtures of a urea and of a phenol with an aldehyde, or polymer of an aidehyde, as described. in my copending application entitled "Method of making plywood", Serial No. 741,745, filed August 2'1, 1934.

In addition to the examples of aqueous binder solutions given in the aforesaid application. the following will serve to illustrate methods of preparing suitable binder solutions:

lmmple 1 Partshyweight Cresylic a Formaldehyde (40% aqueous solution) 1000 Vegetable protein 300 'Ihevegetableproteinmsybeadryextracted soya bean dour, peanut flour, or the like. Such 65 flourisiirstaddedtothecresylicacidwithconstant stirring until a smooth homogeneous mass results. A 38 36. solution of caustic soda, containing about 100 parts of caustic soda, is added tothemixtureofcresylicacidandsoyabeanor the vegetable flour. Then the soya bean oil and triethanolamine are added and the mixture agitated until a smooth homogeneousmass results. The mass is then cooled to 60' I"., at which temperature the formaldehyde is added and the whole mixture agitated for 5 minutes. The heat of reaction between the various ingredients normally brings the mass up to about to C., where the mass is maintained for about 25 to 35 minutes. Next a cold, 10' B. solution of 60 parts 70 ofcausticsodainmpartsofwaterisaddedto the mass. If desired, the solution may be further diluted by the addition of water without causing a precipitation of the partial condensation produetandwillremainstableforalongperiodof 75 time without any increase in viscosity.

Inmakingupthissecondformula,00partsof caustic soda are dissolved in order to form a 30 ne. solution and this solution then added to the cresylic acid and mixed thoroughly therewith. The mixture is allowed to cool to 60' 1!, at which temperature the soya bean oil and triethanolamine are added. 'The iormaldehyde is next added and the mixture agitated. The heat of reaction betweenthe various ingredients brings themassuptoatemperatureofnormallyfrom 70 to' C. Aftermaintainingthemassatthis temperaturefor about 25to 35.minutes,the remaining portion of caustic soda. namely 36 parts, dissolved in 1500 parts of water and having a speciiic gravity of about 10' Be is added to the mixture with constant stirring until cold. As before, the solution may be diluted further by u the addition of water without causing a precipitation of the partial condensation product. The nnalmixtureisaclearambercoloredsolution and will remain stable foralong period'of time without any increase in viscosity.

An improved binder solution may be prepared in accordance with the following example:

trample) Afterthe-reactionmixturehasbeenprepared, but before its diluting withtheadditional-water. the partial condensation product is precipitated by the addition of a'cidulated water. with constant stirring, and then allowed to settle. After decantingoflthesupernatantliquonthesdtae resin material remaining is washed by the further addition oi water until the mixture shows noacidreactiomafterwhichthereainommassis dissolvedinthecausticsodasohitionwithcmstantstirring. 4|

Bythemethodofmmpleaalltheimpuritic areremovedfrom thereaimsotlmtwhentll resinisbroughtbackintosohrtiomthemixture ismuchlighterincolorandholdsioramueh longerperiodofiimewithoutanyincreaseinl. viscosity.

lnkxampleaiandlmbeanflourwpealllt iiourareincorporatedfor'thepurmoiincleasingthebondingstrengthofthesyntheflereln resultingfromthereactionbetweencresylieacid ll and-formaldehyde. Other vegetable products richinprotein, celluloseandcarbohydratesmy beused.

It will be understood that the propel-tins at the various ingredients in the formulae of lx- I amples1and2maybevariedconsiderablyand other ingredients substituted for those enumerated.;as more fully explained in my copendim application above referred to. The caustic soda usedsids'inincreasingthesolubilityoftheinitial I condensation product produced by the reaction between formaldehyde and cresylic acid, I sodium cresylate. Thetriethanolaminawhiehmay be a commercial mixtureoi tri-, di-andmonoethanolamine, acts as an emulsifying asent to I. prevent precipitation of the partial condensation product. It is important to note, however. that thennalsolutionofthehindermaterialisatrue aqueous solution and no'tanemulsionorcoilddal suspension. Thereactionisnotcarriedbeyond fl the point at which the partial condensation product is still water soluble.

I am aware that numerous details of the process may be varied through a wide range without departing from the principles of this invention, and I, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. The method of making laminated products, which comprises impregnating a porous flexible fibrous web with an aqueous solution of a resinous partial condensation product, drying the impregnated web, humidifying said impregnated web to impart thereto a moisture content of from 20 to 40%, laying said humidified web between sheets of the material to be laminated and subjecting the assembled sheets and web to suflicient heat and pressure to efiect a bond therebetween.

2. The method of making laminated products, which comprises impregnating a porous flexible fibrous web with an aqueous solution of a partial condensation product of cresylic acid and an aldehyde, drying the impregnated web, humidifying said impregnated web to impart thereto a moisture content of from 20 to 40%, laying said humidified web between sheets of the material to be laminated, subjecting the assembled sheets and web to suflicient heat and pressure to efiect a bond therebetween and humidifying the resulting laminated product to impart thereto a moisture tween wood veneers and subjecting the veneers and sheet to sufiici'ent heat and pressure to convert the partial condensation product into an infusible resin firmly bonding the laminations together.

JAMES V. NEVIN. 

